Demand for high-speed optical transceiving apparatuses is increasing. For example, an optical phase modulation mode is known as a mode for increasing the multiplicity of a single signal. For example, Quadrature Phase Shift Keying (QPSK) using four-valued phase modulation is conventionally applied to an optical transceiving apparatus.
For faster transmission of transmission signals, an optical polarization multiplexing technique is being developed. The optical polarization multiplex is a mode utilizing two polarized waves having the same wavelengths and orthogonal to each other, for example. A technique is known that reduces an intensity deviation between polarized waves of signal light transmitted from an optical transmitting device of a polarization multiplexed optical transceiving apparatus (see, e.g., Japanese Laid-Open Patent Publication Nos. 2011-44906 and 2011-28087).
However, the conventional techniques have a problem of deterioration in transmission characteristics due to deviation of optical signal-noise ratio (OSNR) between polarized waves even when intensity deviation between polarized waves is reduced.